KR100589898B1 - Method for uplink frame constructing and method for subcarrier allocation in ofdma system - Google Patents

Abstract

The present invention relates to an uplink frame configuration method and a subcarrier allocation method in an OFDMA system. In particular, the present invention relates to an uplink frame configuration method in an OFDMA system for operating a ranging symbol independently from an OFDM symbol for cellular data transmission. It relates to a subcarrier allocation method.

In the method of configuring an uplink frame in an OFDMA system according to the present invention, a signal is transmitted between a first valid symbol section in which actual data is transmitted and a signal inserted at a front end of the first valid symbol section, and in a part of the first valid symbol section. A plurality of uplink OFDM symbols are configured with a first cyclic prefix, and a ranging symbol for uplink ranging shorter than the length of the uplink OFDM symbol is arranged in front of the plurality of uplink OFDM symbols. .

In this case, since the data and the ranging do not use the same OFDM symbol, it is possible to prevent deterioration of system performance due to the performance difference between the power control of the data signal and the power control of the ranging signal.

OFDMA, ranging symbol, OFDM symbol, CP, valid symbol period, frame, uplink

Description

Uplink frame composition method and subcarrier allocation method in OPDMA system {METHOD FOR UPLINK FRAME CONSTRUCTING AND METHOD FOR SUBCARRIER ALLOCATION IN OFDMA SYSTEM}

1 illustrates a frame structure in IEEE 802.16d / e OFDMA mode.

2 illustrates a ranging channel structure currently used in IEEE 802.16d / e OFDMA mode.

3 illustrates data and ranging signal waveforms in a ranging channel structure used in the IEEE 802.16d / e OFDMA mode.

4 is a diagram illustrating a method of configuring an uplink frame according to an embodiment of the present invention.

5 is a diagram illustrating a subcarrier allocation method for ranging symbols according to an embodiment of the present invention.

The present invention relates to the configuration of a ranging symbol for initial ranging in an orthogonal frequency division mutiplexing access (OFDMA) system. In particular, the present invention improves ranging and bit error rate (BER) performance in an OFDMA system. The present invention relates to an uplink frame configuration method and a subcarrier allocation method for ranging symbols.

Channel environment for wireless communication has multipath due to obstacles such as buildings. In a multipath radio channel, multi-path delay spread occurs and inter-symbol interference (ISI) occurs when the delay spread time is larger than the time when the next symbol is transmitted. In this case, frequency selective fading occurs in a frequency domain. When one carrier is used, an equalizer is used to remove inter-symbol interference. However, as the speed of data increases, so does the complexity of the equalizer.

Therefore, recently, an OFDM (Othogonal Frequency Division Multiplexing) method using multiple carriers has been in the spotlight as a transmission technology for supporting a high-speed transmission service of wired and wireless communication.

In OFDM (Othogonal Frequency Division Multiplexing) system, a type of multicarrier transmission using multiple carriers, the transmission period of each channel is increased by the number of carriers. In this case, since the frequency selective channel appearing in the wideband transmission is approximated as a frequency non-selective channel without intersymbol interference, a simple single tap equalizer can compensate for intersymbol interference.

Also, in terms of system complexity, the modulation and demodulation process of the OFDM transmitter and receiver is the same as that of IDFT and DFT, respectively, so that a high speed system with low implementation is possible. In addition, the OFDM system processes the data by transmitting high-speed data in parallel using a plurality of subcarriers, thereby reducing the sensitivity to impact noise. By using a low-speed parallel carrier, the symbol interval is increased, thereby reducing the ISI. In addition, the use of guard intervals almost completely eliminates ISI and provides high spectral efficiency by orthogonally overramping the frequency.

In such an OFDM system, N parallelized data symbols are modulated by a corresponding carrier, and the result is added to form an OFDM symbol. Finally, the OFDM system is inputted to an RF terminal and transmitted to a channel.

An OFDM symbol is composed of a plurality of subcarriers including a pilot subcarrier and a data subcarrier used for a null subcarrier and a channel estimation, which constitute a DC and a guard interval, and small information when the subcarriers cannot be divided and used. When transmitting the full OFDM symbol should also be used.

On the other hand, as a multiple access scheme for multiple users of an OFDM system, Orthogonal Frequency Division Modulation / Multiplexing Access (hereinafter referred to as 'OFDMA') is a subcarrier in which multiple users configure OFDM symbols in uplink. By dividing the number of subcarriers according to the transmission rate required by each user, more detailed resource allocation is possible, which enables efficient resource distribution, saves frequency resources, and allocates allocated resources. Power can be concentrated in the system to increase coverage.

Since the OFDMA scheme is suitable for a large number of subcarriers (that is, a large FFT size), the OFDMA scheme is effectively applied to a wireless communication system having a large area cell having a relatively large time delay spread. The locations of users in a cell are randomly distributed, and when subcarriers are divided from uplink, subcarrier groups for each user arrive at different times and have different powers. Therefore, the main purpose of ranging in OFDMA is to eliminate this problem and perform two functions of timing acquisition and power control.

As a technique related to the initial ranging of the OFDMA system, Korean Patent Laid-Open No. 2001-0089103 discloses "Interval and Raising Channel Allocation Method for Initial Raising of Orthogonal Frequency Division Multiple Access System". This technique provides ranging intervals and lanes for initial ranging from a multi-user Orthogonal Frequency Division Multiple Access (OFDMA) wireless communication system in a Point-to-MutiPoint Broadband Wireless Access BWM system. The present invention relates to a method for allocating a subchannel, wherein a specific time consisting of a predetermined number of OFDM symbols as an initial ranging interval in a MAC for removing interference on a data subchannel due to a long ranging subchannel during an initial ranging process. Specifies slots. In addition, four new initial ranging subchannel allocation methods for performing the initial ranging function according to the ranging intervals can be used to prevent interference between signals for initial ranging and signals for data transmission, and to reduce resources. There is an advantage that can be operated efficiently.

Initial Ranging of IEEE 802.16d / e OFDMA currently uses some subcarrier groups designated from two OFDM symbols. Subcarrier groups that are not used for initial ranging from two OFDM symbols are used for data transmission.

1 illustrates a frame structure in IEEE 802.16d / e OFDMA mode.

As shown in FIG. 1, the frame is composed of TTG / RTG which does not transmit between uplink, downlink and uplink and downlink. The uplink consists of a plurality of uplink OFDM symbols, and the downlink consists of a preamble and a plurality of downlink OFDM symbols.

At this time, some subcarrier groups constituting the first two OFDM symbols constituting the uplink is used for uplink initial synchronization acquisition and power control.

That is, as shown in FIG. 1, some subcarriers of the first two OFDM symbols transmit data and the other subcarriers are used for ranging.

2 illustrates a ranging channel structure currently used in IEEE 802.16d / e OFDMA mode.

As shown in FIG. 2, in general, an initial synchronization is obtained by receiving a Pseudo-Noise (PN) code generated by a base station. In IEEE 802.16d / e, a PN code is transmitted using a subcarrier allocated for ranging. Since no synchronization is obtained at first, the same PN code is transmitted over two OFDM symbol intervals. In order to prevent a sudden phase change during the ranging period, a cyclic prefix is inserted in the first OFDM symbol and a post prefix is inserted in the second OFDM symbol during the continuous ranging period.

3 illustrates data and ranging signal waveforms in a ranging channel structure used in the IEEE 802.16d / e OFDMA mode.

As shown in FIG. 3, initial ranging in the current IEEE 802.16d / e OFDMA uses a subcarrier group designated in two OFDM symbols, and a subcarrier group that is not used for initial ranging in two OFDM symbols is used for data transmission. As used herein, data and ranging signals exist simultaneously in two consecutive OFDM symbol intervals.

In this structure, the PN codes for ranging in two consecutive OFDM symbols are the same, but data transmitted in the first OFDM symbol and the second OFDM symbol are different. As such, if data transmissions are not the same during two OFDM symbol periods, phase discontinuity occurs in a period t2, and the interference caused thereby affects the ranging performance. In addition, since the phase of the ranging signal is discontinuous in the interval t1, the data BER performance is degraded. Since the ranging signal penetration in the intervals t3 to t5 acts as an ISI on the third OFDM symbol, the data BER performance of the third OFDM symbol is degraded. Causes deterioration.

SUMMARY OF THE INVENTION The present invention provides a method for configuring an uplink frame in an OFDMA system that can eliminate data BER degradation due to a phase discontinuity of a ranging signal, a phase discontinuity of a data signal, and a penetration of a ranging signal into the next OFDM symbol. And a subcarrier allocation method.

In order to solve this problem, the present invention provides an uplink frame configuration method and subcarrier allocation method in an OFDMA system.

According to an aspect of the present invention, a method of configuring an uplink frame in an OFDMA system includes:

An uplink frame configuration method for ranging in an orthogonal frequency division mutiplexing access (OFDMA) system,

a) a plurality of upwards with a first cyclic prefix, which is inserted at the front end of the first valid symbol section to which actual data is transmitted and copied in a signal of a partial section of the first valid symbol section; Constructing OFDM symbols respectively; And b) disposing a ranging symbol for uplink ranging shorter than a length of the uplink OFDM symbol in front of the plurality of uplink OFDM symbols.

In this case, step b) may include: arranging a second valid symbol section shorter than a first valid symbol section of the uplink OFDM symbol in front of the first transpose; And inserting a second pre-cycle longer than the first pre-cycle of the uplink OFDM symbol in front of the second valid symbol interval.

According to another aspect of the present invention, a subcarrier allocation method in an OFDMA system includes

A subcarrier allocation method for a ranging symbol used for ranging in an orthogonal frequency division mutiplexing access (OFDMA) system,

a) allocating 1 / N of all subcarriers as subcarriers for ranging; And b) allocating one subcarrier for insertion of a pseudo-noise (PN) code among the adjacent N subcarriers, and does not transmit other subcarriers except for one subcarrier for transmission of the PN code. .

In this case, the ranging symbol is 1 / N times shorter than the length of one OFDM symbol formed by modulating data symbols by the corresponding subcarrier.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention. Like parts are designated by like reference numerals throughout the specification.

Now, an uplink frame configuration method and a subcarrier allocation method in an OFDMA system according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

The OFDMA system modulates N parallelized data symbols by corresponding carrier using QPSK, 8-PSK differentially coded in the frequency domain as a modulation scheme, or optionally 16-QAM scheme in synchronous mode, and adds the result to one OFDM signal. It forms a symbol and is finally input to the RF stage and transmitted to the channel.

The transmission of the OFDM symbol is performed in symbol units, but is affected by the previous symbol while the OFDM symbol is transmitted through the multipath channel. In order to prevent such ISI, a guard interval longer than the maximum delay spread of a channel is inserted between consecutive OFDM symbols. Therefore, the OFDM symbol period is the sum of the effective symbol period and the guard period for transmitting the actual data. In order to prevent the destruction of orthogonality caused by the delay of the subcarrier, the guard section copies and inserts the signal of the last section of the valid symbol section, which is called a cyclic prefix (CP). . The insertion of the CP reduces the bandwidth efficiency and causes a loss of the signal-to-noise ratio of the effective symbol interval. Therefore, the length of the effective symbol section is set so that the signal-to-noise ratio loss due to the insertion of the CP is 1% or less.

In such an OFDMA system, initial modulation timing synchronization, modulation timing tracking, initial frequency offset synchronization, and frequency tracking should be considered for uplink and downlink.

In particular, initial timing synchronization is necessary to adjust the internal timing of the mobile station to the base station time frame. After detecting the timing of the base station, when a random access channel (RACH) packet is transmitted to the base station, the base station measures the timing offset. Return timing information to the mobile station.

In addition, since the OFDMA system maintains the size of the received signal of the base station by performing power control in the uplink, the total power required to support a specific quality of service can be reduced to a minimum level.

In an OFDMA system, ranging performs two functions such as timing acquisition and power control.

According to an embodiment of the present invention, a ranging dedicated OFDM symbol (hereinafter, referred to as 'lane') using a CP longer than a CP used by an OFDM symbol for actual data transmission and having a shorter valid symbol period than an OFDM symbol for actual data transmission. Gong symbol ') is used independently for ranging.

4 is a diagram illustrating a method of configuring an uplink frame according to an embodiment of the present invention.

As shown in FIG. 4, the frame includes TTG / RTG which does not transmit between uplink, downlink and uplink and downlink.

The uplink consists of a plurality of uplink OFDM symbols for data transmission and a ranging symbol located at the front end of the plurality of uplink OFDM symbols, and the downlink consists of a preamble for channel estimation and a plurality of downlink OFDM symbols for data transmission. do.

The uplink or downlink OFDM symbol consists of a valid symbol interval and a transpose cycle.

The valid symbol section is a section in which data symbols are modulated and actual data is transmitted, and has a specific valid symbol period.

The transposition loop inserts a portion of the effective symbol section repeatedly at the front end of the effective symbol section to prevent orthogonal destruction caused by delay of the subcarrier.

In addition, the ranging symbol according to the embodiment of the present invention has a valid symbol period shorter than the OFDM symbol for actual data transmission without using two OFDM symbols for initial ranging as in the IEEE 802.16d / e OFDMA mode. A dedicated OFDM symbol in which a CP longer than the CP used by the OFDM symbol for actual data transmission is inserted before the symbol period is used.

At this time, the ranging symbol is shorter than the OFDM symbol for actual data transmission and is located at the front of the uplink frame. The length of the CP of the ranging symbol is sufficiently long in consideration of delay spread of the channel and up-down bidirectional delay.

5 is a diagram illustrating a subcarrier allocation method for ranging symbols according to an embodiment of the present invention.

As shown in FIG. 5, if a ranging symbol allocates 1 / N of all subcarriers for ranging, only one subcarrier 10 of every adjacent N subcarriers transmits a PN code, and the remaining (N− 1) subcarriers 20 are not used. This makes it possible to create a 1 / N ranging symbol.

As such, the ranging symbol according to the embodiment of the present invention is an OFDM symbol that is 1 / N times shorter than an OFDM symbol length for normal data transmission, and does not use two OFDM symbols as shown in FIG. By creating a symbol and operating it as a ranging symbol independently, it is possible to prevent deterioration of system performance due to a difference in performance between uplink power control of a data signal and power control of a ranging signal.

For example, if 1/6 of all subcarriers are allocated for ranging, a PN code for ranging is inserted into one subcarrier of six adjacent subcarriers, and the remaining five subcarriers are not used. This makes it possible to create ranging dedicated OFDM symbols of length 1/6.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

According to the present invention, BER degradation due to phase discontinuity of the ranging signal can be prevented, and degradation of ranging performance due to phase discontinuity of the data signal can be prevented.

Then, BER degradation of data due to ISI caused by penetration of the ranging signal into the OFDM symbol can be prevented. When data and ranging use the same OFDM symbol, power control of the data signal and power control of the ranging signal are performed. It is possible to prevent the performance degradation of the system due to the difference in performance.

In addition, by using one short OFDM symbol instead of two OFDM symbols, it is possible to prevent waste of frequency resources.

Claims (10)

A method of configuring an uplink frame for ranging in an orthogonal frequency division mutiplexing access (OFDMA) system, a) a plurality of upwards with a first cyclic prefix, which is inserted at the front end of the first valid symbol section to which actual data is transmitted and copied in a signal of a partial section of the first valid symbol section; Constructing OFDM symbols respectively; And b) disposing a ranging symbol for uplink ranging shorter than a length of the uplink OFDM symbol in front of the plurality of uplink OFDM symbols Uplink frame configuration method in an OFDMA system comprising a. The method of claim 1, Step b), Disposing a second valid symbol section shorter than a first valid symbol section of the uplink OFDM symbol in front of the first transpose; And Inserting a second transpose longer than the first transpose of the uplink OFDM symbol in front of the second valid symbol interval; Uplink frame configuration method in an OFDMA system comprising a. The method of claim 2, The length of the second pre-cyclic cycle is configured based on the delay spread of the channel and the uplink and downlink bidirectional delay method of the uplink frame in the OFDMA system. A subcarrier allocation method for a ranging symbol used for ranging in an orthogonal frequency division mutiplexing access (OFDMA) system, a) assigning 1 / N of the total subcarriers, where N is any natural number, to the subcarriers for ranging; And b) allocating one subcarrier for the insertion of a pseudo-noise (PN) code among the adjacent N subcarriers Including; The subcarrier allocation method in the OFDMA system does not transmit the other subcarriers except one subcarrier for the transmission of the PN code. The method of claim 4, wherein The ranging symbol is a subcarrier allocation method in an OFDMA system, which is 1 / N times shorter than the length of one OFDM symbol configured by modulating data symbols by a corresponding subcarrier. The method of claim 5, The OFDM symbol is A valid symbol section having a first valid symbol period in which the data symbols are modulated and actual data is transmitted, and a part of the valid symbol section is repeated in order to prevent orthogonal destruction due to a delay of the subcarrier. A subcarrier allocation method in an OFDMA system comprising a first cyclic prefix (CP) inserted into a subframe. The method of claim 6, The ranging symbol is a subcarrier allocation method in an OFDMA system having a valid symbol period shorter than the first valid symbol period and a transposition longer than the first precycle. The method of claim 7, wherein The ranging symbol is a subcarrier allocation method in an OFDMA system in which the pre-circulation is arranged in front of the valid symbol period. The method of claim 8, The ranging symbol is a subcarrier allocation method in an OFDMA system located in front of an uplink frame. The method according to any one of claims 4 to 9, And the total number of subcarriers is equal to the number of subcarriers included in one OFDM symbol configured by data symbols modulated by the corresponding subcarrier.

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